MEA is an integral assembly generally consisting of an electrolyte membrane (proton conductive membrane) and electrode substrates. Conventional production of MEA has been carried out by sandwiching an electrolyte membrane between two electrode substrates and hot pressing them to form an anode/electrolyte/cathode assembly.
Proton conductive membranes based on sulfonated perfluorohydrocarbon, typically Nafion® membranes, are thermoplastic and can be thermocompression bonded with electrodes. On the other hand, electrolyte membranes of aromatic polymers such as sulfonated polyarylenes have heat resistance so that the thermocompression bonding often fails to achieve sufficient bond strength unless carried out at high temperatures that will cause deterioration of metallic catalysts.
Film casting is a method to make electrolyte membranes by flow casting a solution of a polymer in an organic solvent on a substrate, followed by drying the formed coating. In the film casting method, highly dipolar and aprotic organic solvents are generally used to dissolve highly polar polymers with ion-exchange groups, such as proton conductive polymers. These dipolar solvents, due to their high boiling points, are not completely removed upon drying and as a result remain in the final electrolyte membranes. The electrolyte membranes that contain such polar solvents in high concentrations cannot be adequately thermocompression bonded with electrode substrates, causing poor interlaminar bond strength of MEA.